This Little Camping Hack May Save Your Life If You Get Lost In The Woods. When you are alone or get separated from a group, this acorn whistle trick may help your group mates find you.
As explained in more details here at wikihow, an acorn cap help you blow very loud whistle. Practice this trick when you find an acorn cap until you can master the technique. Next time when you go out and lost in woods, at least you have something to try.